In general machines having a hopper for supplying materials, such as, a plastic resin kneading and extruding machine, the inside of the hopper is cleaned directly when the cleaning of the hopper is needed with time. Such a conventional manner has such defects that much labor and time must be necessary and accordingly the working efficiency is reduced. The background of the present invention is to realize a hopper and a processing method thereof which reduce the labor and time for the cleaning of the hopper without reducing the working efficiency.